1. Field of the Invention
The present invention relates to a method and system for preventing call loops for wholesale VoIP traffic when multiple carriers are involved in handling the same phone call.
2. Description of the Related Art
The existence of call loops is well known in the phone industry. For example: A has call forwarding set to call B, B has call forwarding set to call C, and C has forwarding set to call A. As soon as somebody calls A the call goes into an infinite loop. The Public Switched Telephone Network (PSTN) has relatively slow call setup (seconds) and that loop can be propagated only up to some limited level. By the time that the loop would become dangerous, the caller would have hung up the phone and broken the loop. This is also typically the case when the loop is created by end user devices, not Telco switches.
However, the situation is different in the case of Voice over Internet Protocol (VoIP). With call speeds reaching thousands of calls per second, the loop can reach hundreds of thousands of calls before it is terminated. In addition, there is no transitional header in the SIP message that can indicate that call is not a new call, but actually was triggered by another call.
In addition, unlike the traditional PSTN network, VoIP carriers have a much higher level of interconnectivity and it is quite common that carrier A provides services to carrier B as well as using carrier B to terminate the service, quite often into the same area. Even more, multiple carriers can be involved in the traffic exchange and the resulting loop can be quite long.
One of the limitations of SIP messaging is the absence of a permanent header that would be preserved between different carriers to uniquely identify the call. The existing Call-ID can be replaced by any SIP User Agent (any intermediate carrier could, and usually does, have one) and is not preserved and no alternative header is provided.
As a result, a need arises for a technique to prevent call loops for wholesale VoIP traffic when multiple carriers are involved in handling the same phone call.